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. 2020 Dec 4;21(23):9266. doi: 10.3390/ijms21239266

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© 2020 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Scheme 2 — Mechanism of main COVID-19 protease inhibition by celastrol. P_a and P_b represent the peptide chain associated with Cys145. Only three rings of celastrol are shown for clarity. (1) HN(His41) donates a proton to celastrol carbonyl; (2) O(His146) captures HS(Cys145), generating the S(Cys145) thiolate. Joining products of steps (1) and (2) generates species (3) that stabilizes the S-C(carbonyl) covalent bond; (4) Met49 points to celastrol ring B centroid; (5) Met49 forms a S-π interaction with ring B centroid, so that celastrol finally establishes a double interaction with Cys145 and Met49, of the COVID-19 protease.